[tgamblin]

FWIW, we do something like this in Spack[1] with `spack config blame`. There are different YAML configs, they can be merged and override each other based on precedence, but we tell you where all the merged values are coming from. Here's a simplified example -- you can see that some settings are coming from the user's "default" environment, some from Spack's defaults, and some from specialized defaults for Darwin:

    > spack -e default config blame packages
    ---                                               packages:
    spack/environments/default/spack.yaml:59            fftw:
    spack/environments/default/spack.yaml:60              require: ~mpi
    spack/etc/spack/defaults/darwin/packages.yaml:17    all:
    spack/defaults/packages.yaml:18                       compiler: [apple-clang, gcc, clang]
    spack/defaults/darwin/packages.yaml:20                providers:
    spack/defaults/darwin/packages.yaml:21                  unwind: [apple-libunwind]
    spack/defaults/packages.yaml:20.                        blas: [openblas, amdblis]
    spack/defaults/packages.yaml:21                         jpeg: [libjpeg-turbo, libjpeg]
    spack/defaults/packages.yaml:22                         lapack: [openblas, amdlibflame]
    spack/defaults/packages.yaml:23.                        mpi: [openmpi, mpich]
    spack/defaults/darwin/packages.yaml:22              apple-libunwind:
    spack/defaults/darwin/packages.yaml:23                buildable: False
    spack/defaults/darwin/packages.yaml:24                externals:
    spack/defaults/darwin/packages.yaml:27                - spec: apple-libunwind@35.3
    spack/defaults/darwin/packages.yaml:28                  prefix: /usr

The filenames are shown in color in the UI; you can see what it really looks like here: https://imgur.com/uqeiBb5

For the curious, there is more on scopes and merging [2]. This isn't exactly easy to do -- we use ruamel.yaml [3], but had to add our own finer-grained source attribution to get this level of detail. There are also tricky things to deal with to maintain provenance on plain old Python dict/str/list/etc. objects [4,5].

[1] https://github/spack/spack

[2] https://spack.readthedocs.io/en/latest/configuration.html

[3] https://yaml.readthedocs.io/en/latest/

[4] https://github.com/spack/spack/blob/95ca9de/lib/spack/spack/...

[5] https://github.com/spack/spack/blob/95ca9de/lib/spack/spack/...